design and development of a secure wireless ... - ePrints@USM
design and development of a secure wireless ... - ePrints@USM
design and development of a secure wireless ... - ePrints@USM
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signals with the PN sequence (Simon et al., 1985). However, in-b<strong>and</strong> pulse RFI,<br />
e.g., a radar signal whose frequency is in the desired signal data b<strong>and</strong>, can<br />
seriously degrade the PN system which is operating in a linear channel,<br />
because peak power <strong>of</strong> the pulse RFI is much stronger than the PN spread<br />
signal power. Hence, a s<strong>of</strong>t-limiter at the front end <strong>of</strong> the receiver has been<br />
used for second generation transponder, which is also recommended for the<br />
<strong>design</strong> <strong>of</strong> the Space Station Freedom (SSF) S-b<strong>and</strong> PN system.<br />
Several methods have been proposed for the calculation <strong>of</strong> the effect <strong>of</strong><br />
memoryless non-linearties on the sum <strong>of</strong> input signals. Of these, the transform<br />
method (Davenport <strong>and</strong> Root, 1958; Blachman, 1971) is widely applicable. For<br />
PN spread-spectrum signals, this method cannot give a complete analysis<br />
because it does not supply phase information about the output signals (Baer,<br />
1992). A modified transform method which use the transfer characteristic <strong>of</strong> the<br />
nonlinear device as suggested by Davenport <strong>and</strong> Root (1958) <strong>and</strong> apply a timedomain<br />
approach has been used to study interference effects <strong>of</strong> hard-limiting in<br />
PN spread-spectrum systems ( Baer,1992).<br />
2.3.2 Fast Frequency Hopping Spread Spectrum <strong>and</strong> Jamming Systems<br />
Spasojevic <strong>and</strong> Burns (2000) presented the report analyses <strong>of</strong> two main spread<br />
spectrum (SS) technologies used by <strong>wireless</strong> devices in the 2.4GHz ISM b<strong>and</strong>.<br />
The authors compared the technical characteristics <strong>of</strong> frequency hope spread<br />
spectrum (FHSS) <strong>and</strong> direct sequence spread spectrum (DSSS). They used<br />
indoor <strong>and</strong> outdoor radio local area network (RLAN) densities <strong>of</strong> 100 <strong>and</strong> 1 per<br />
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